Bug 1533744 - Properly gate anyref. r=luke
When I removed the guard on anyref for gcTypesEnabled I should have added a couple
more ifdefs so that anyref is only accepted when the reftypes are enabled.
This patch adds those guards, and expands test cases that check that the feature
is properly disabled to include more possible error messages.
Differential Revision: https://phabricator.services.mozilla.com/D22893